Well you have to consider a few things. First of all, it doesn't matter how much your head unit costs. Installing a head unit and integrating it with all the steering wheel controls and car AV system these days is not an easy job. It requires a few pieces of hardware, installing a few harnesses, and taking apart a lot of interior body panels. If they damage any of these, they have to insure everything to make sure they can fix anything that breaks. No matter how good a shop is, shit breaks. Finally, SJ is just a very expensive place. I lived in the peninsula for 7 years and everything there just as the "bay area tax."

The most important thing, however, is that you can bargain at A/V install places. Much of the cost is labor. For small shops where they only have one or two main installers who may or may not be the owner of the shop, the install fee is almost pure profit. So they're usually willing to come down on the price if you say you're gonna shop around.

The most honest thing to do is to call around to another shop (look at Yelp reviews) and get a few quotes over the phone or in person. I've learned over the years that the absolute strongest bargaining chip is shopping around. They don't want you to shop around. Just tell them you'll go to another shop to get a quote and they might just give you a discount right then and there. If not, just shop around and see who gives you the best rate.

Yelp can be pretty shady, but it really can help to find a good auto repair, body shop. tint shop, tire shop, or any automotive related shop in general.